1. Field Of The Invention
The present invention relates to semiconductor integrated circuits, and more particularly to input/output driver circuits for integrated circuits.
2. Background Art
U.S. Pat. No. 4,855,623 issued Aug. 8, 1989 to Flaherty entitled OUTPUT BUFFER HAVING PROGRAMMABLE DRIVE CIRCUIT discloses an output buffer circuit for providing selected output driving characteristics. A plurality of input terminals receive control and data signals and are connected to an output terminal through a plurality of interconnected driver transistors. Drive selector circuitry is responsive to control signals to selectively vary the connections of the driver transistors to the output terminal.
U.S. Pat. No. 5,153,450 issued Oct. 6, 1992 to Ruetz entitled PROGRAMMABLE OUTPUT DRIVE CIRCUIT discloses a programmable output driver circuit having multiple drive capabilities for optimizing noise margins at different frequencies. The circuit includes a plurality of signal paths in parallel, each comprising a driver unit having a pull-down and pull-up transistor. During operation, selected signal paths are disabled to reduce noise at lower frequencies.
U.S. Pat. No. 5,486,782 issued Jan. 23, 1996 to Chan entitled TRANSMISSION LINE OUTPUT DRIVER discloses a push-pull output driver circuit that includes a pair of low current output circuits connected in parallel with a pair of high current series connected devices. In response to a pulse transition at the driver circuit input, one of the high current devices is turned on to change the state of the output signal. When the output signal has reached a steady state, a low current device is turned on and the high current device is turned off such that the low current maintains the output signal state.
U.S. Pat. No. 5,498,977 issued Mar. 12, 1996 to Pickup entitled OUTPUT DRIVER HAVING PROCESS, VOLTAGE AND TEMPERATURE COMPENSATION FOR DELAY AND RISETIME discloses a chip wherein the effects of Process, supply Voltage and Temperature (PVT) variables are minimized by a table of predrive gain used to compensate for the effect of the PVT variables.